1. Field of the Invention
This invention relates generally to railroad maintenance and, more particularly, to methods of surveying railroad track beds in conjunction with position recording and performing track maintenance operations, such as maintenance of drainage ditching along the track bed, based on the survey results.
2. Background & Description of the Related Art
Conventional railroads in the United States and elsewhere are formed by a compacted subgrade, a bed of gravel ballast, wooden cross-ties positioned upon and within the ballast, and parallel steel rails secured to the ties. Variations of construction occur at road and bridge crossings, at switch points, and in other circumstances. The ballast beneath and between the ties stabilizes the positions of the ties, keeps the rails level, and provides some cushioning of the composite structure for loads imposed by rail traffic. Ballast in good condition is porous which allows rainwater and snow melt to drain through it and away from the railroad. This is desirable because standing water in the ballast can cause deterioration of the track and ties, the ballast, and the subgrade.
Water from the ballast needs to be drained away from the subgrade. To accomplish this, a ditch may be formed along one or both sides of a railway. The ditch line should be sloped slightly, to positively drain water toward a drainage point, which may be a natural body of water, a drainage structure such as a culvert, or the like. If the ditch is not constructed properly, water can pool up or drain away to an unforeseen location, possibly causing undesired effects such as erosion or the like.
Conventional ditch construction and maintenance can be laborious, often requiring surveying type measurements to maintain an accurate pitch of the ditch line. Although initial ditch construction can be automated, such as by the use of machinery similar to those shown in U.S. Pat. Nos. 4,723,898 and 4,736,534, which are incorporated herein by reference, ditch maintenance may require not only removal of soil material but also the replacement of soil which has been eroded away.
Methods for automated surveying for ballast maintenance are known. Such methods often employ LIDAR (light detection and ranging) scanning of the railway along with concurrent recording of position coordinates, such as by GPS (global positioning system) or GNSS (global navigation satellite system), IMU (inertial measurement unit), wheel encoders, or combinations thereof. Such automated surveying methods typically generate graphic ballast profiles which can be used to determine amounts of ballast needed to replace ballast which has been dislodged by vibrations, weather, and the like. Methods for spreading railroad ballast with location control based on data received from position coordinate systems are disclosed in U.S. Pat. Nos. 6,526,339 and 7,152,347, which are incorporated herein by reference.